1. Field of the Invention
The present invention relates to method and apparatus for measuring a pitch of a stranded cable, and more particularly to method and apparatus capable of measuring a pitch for a spirally stranded structure of a cable in real time at a low cost.
1. Description of the Related Art
A communication cable is generally manufactured by stranding at least two wires. At this time, it is important to strand the wires at regular pitches along a longitudinal direction in order to improve transition characteristics especially Near End Cross-Talk (NEXT) and Return Loss (RL).
FIG. 1 is a schematic view showing a conventional apparatus for manufacturing a stranded cable 2.
Referring to FIG. 1, the apparatus for manufacturing a stranded cable includes a wire pay-off 10 having a wire bobbin 11 for supplying at least two wires 1, a capstan 25 for drawing the wires 1 at a regular velocity, a guide die 15 and a rotation body 20 positioned between the wire pay-off 10 and the capstan 25, and a take-up device 30 for taking up the stranded cable 2.
The wires 1 continuously supplied from the wire pay-off 10 by drawing of the capstan 25 is transmitted to the take-up device 30 after being stranded through the rotation body 20 in a state of being collected by the guide die 15.
A method for manufacturing a stranded cable by using the conventional apparatus may be classified into, for example, single twister method, double twister method, triple twister method and so on according to the number of pitches per one rotation of the rotation body 20.
Here, it is important to accurately monitor a length of pitch in real time during the stranding process so as to generate regular pitchs along a longitudinal direction of the cable. However, since a means for measuring a pitch of a cable by an in-line method has not been provided in the past, a pitch was generally measured off-line after all processes are finished.
In the off-line method, since the pitch is measured with the naked eye by using a length measurement means such as a micrometer or a vernier calipers, the method has disadvantages that measurement time is too long, and a measurement value error is apt to be generated depending on persons in charge of the measurement.
On the other hand, since inferiority of the pitch generated during stranding process cannot be detected in real time, the conventional method has a disadvantage that operating conditions affecting on the pitch state cannot be adequately set. For example, in the fact that a pitch of the cable is continuously changed by a change of tensile force acted on the wire and a change of a ratio of wire-velocity to the rotation body frequency caused by a slip of the wire in the capstan 25, and so on, the conventional method cannot monitor these changes in real time.